1. Field of the Invention
This invention relates to exhaust nozzles and particularly to a new and improved exhaust nozzle which is effective for varying the size of the exhaust opening and for providing a thrust vectoring capability.
2. Description of the Prior Art
Exhaust systems, particularly for modern, high speed, military aircraft, must be capable of providing cruise efficiency and a high degree of maneuverability.
Cruise efficiency can be achieved through the use of a variable geometry exhaust nozzle. A variable geometry nozzle permits the size of the exhaust opening to be changed in response to changes in flight conditions, such as air speed and altitude. However, changing the geometry of an exhaust nozzle can result in areas of high stress, which are caused by the pressure of the exhaust gases, being shifted to portions of the nozzle which are less capable of withstanding such stress. For example, most exhaust nozzles for high speed aircraft employ a converging/diverging exhaust nozzle. By converging/diverging, it is meant that the cross-sectional area of the exhaust nozzle in a downstream direction decreases to a position of minimum area, called the throat, and then increases to the downstream end of the nozzle. Exhaust nozzles are often made variable through the use of a plurality of moveable nozzle sections. Varying the geometry of such a nozzle can move the throat, on which is exerted a high concentration of stress, to a nozzle section which is less capable of withstanding such stress than are other sections. Structural fatigue which results can shorten the useful life of the stressed sections which in turn results in higher cost to the user.
Aircraft maneuverability can be achieved through the use of a vectorable exhaust nozzle. Since the resultant thrust vector of an engine is in a direction opposite to the direction at which the exhaust gases exit the engine exhaust nozzle, by pivotally changing the exit angle of the nozzle, the thrust vector can be correspondingly changed.
Most currently used vectorable exhaust nozzles, however, are limited as to the range of pivotal movement available. For example, two-dimensional nozzles, that is those which define a generally rectangular exhaust opening, are being considered for use on high speed aircraft. Suggested means for thrust vectoring in two-dimensional nozzles have generally been either gimbaling the entire nozzle or pivoting flaps located at the nozzle exit. Either means by itself has a pivotal limitation, due to structural, kinematic, or aerodynamic constraints. Greater degrees of pivotal movement can be achieved by combining flaps with a gimbaled nozzle. However, such a combined nozzle would require complicated hardware and controls and thus be expensive.
Another problem which is encountered in exhaust nozzles which are vectorable or which have a variable geometry is that most are actuated by hydraulically powered servo units. Such servo units, and the associated plumbing and valving, are relatively heavy and space consuming and are costly. Furthermore, the hydraulic lines, particularly in the hostile environment in which a military aircraft might operate, are more vulnerable to being damaged and thereby rendering the servo units inoperative, than would, for example, electrically operated actuators. Additionally, it is very difficult to mount hydraulically actuated pivotable control surfaces in tandem, that is with one pivotable control surface mounted on another pivotable control surface, such as might be desirable to achieve a greater degree of thrust vectoring. Such an arrangement would necessitate the hydraulic lines themselves being pivotable in order to reach the servo unit for the second control surface. Thus, hydraulically actuated exhaust nozzles present numerous limitations.
In view of the above-mentioned problems, it is, therefore, an object of the present invention to provide a variable geometry exhaust nozzle in which the location of the nozzle throat is continually maintained on the structurally strongest portions of the nozzle.
Another object of the present invention is to provide a vectorable exhaust nozzle which has a large range of pivotal movement and yet which is structurally simple and therefore of lower cost.
Yet another object of the present invention is to provide a variable geometry, vectorable exhaust nozzle which utilizes electromechanical actuators and thereby avoids many limitations of hydraulic actuators.